The present invention relates to a process and catalyst for the transalkylation of aromatics, particularly the transalkylation of polyisopropylbenzene with benzene to produce cumene and the transalkylation of polyethylbenzene with benzene to produce ethylbenzene. Ethylbenzene is a valuable commodity chemical and is used in the production of styrene monomer. Cumene (isopropylbenzene) is also a valuable commodity chemical and is used in the production of phenol and acetone.
Presently, ethylbenzene is often produced by a liquid phase alkylation process from benzene and ethylene in the presence of an alkylation catalyst. The liquid phase process operates at a lower temperature than its vapor phase counterpart and, therefore, produces a lower yield of polyalkylated by-products and other impurities. The alkylation of aromatic hydrocarbon compounds employing zeolite catalysts is known and understood in the art. U.S. Pat. No. 5,334,795 describes the liquid phase alkylation of benzene with ethylene in the presence of MCM-22 to produce ethylbenzene; and U.S. Pat. No. 4,891,458 discloses liquid phase alkylation and transalkylation process using zeolite beta.
Zeolite-based catalyst systems are used in the propylation of benzene to cumene. U.S. Pat. No. 4,992,606 discloses a process for preparing short chain alkyl aromatic compounds using MCM-22, including the liquid phase alkylation of benzene with propylene in the presence of MCM-22 to produce cumene.
Alkylation processes in commercial use for the production of ethylbenzene and cumene produce certain polyalkylated by-products in addition to ethylbenzene and cumene. It is well known in the art to transalkylate the polyalkylated by-products with benzene or other alkylatable aromatic to produce additional ethylbenzene or cumene. This transalkylation reaction may be accomplished by feeding the polyalkylated by-products through a transalkylation reactor operated under suitable conditions and in the presence of a transalkylation catalyst. Also, the polyalkylated by-products may be recycled to an alkylation reactor in the presence of an alkylation catalyst that is capable of performing the transalkylation reaction. U.S. Pat. No. 5,557,024 discloses a process for preparing short chain alkyl aromatic compounds using MCM-56 and the use of zeolite catalysts such as MCM-22, zeolite X, zeolite Y and zeolite beta for the transalkylation of the polyalkylated by-products.
Conducting the transalkylation reaction under liquid phase conditions imposes increased demands on the transalkylation catalyst. Heretofore, the transalkylation catalysts of the prior art have lacked desired activity or have not achieved adequate conversion rates for liquid phase transalkylation reactions.
U.S. Pat. No. 5,470,810 discloses that the addition of phosphorus to porous crystalline materials having the x-ray structure of MCM-22 improves the hydrothermal stability of the catalyst to maintain activity after repeated cycles of steaming as experienced in FCC processes.
U.S. Pat. No. 3,962,364 discloses that the addition of at least 0.5 wt. % phosphorus to a crystalline aluminosilicate zeolite, such as ZSM-5 to increase its selectivity for the desired alkylated hydrocarbon in the vapor phase alkylation of aromatic hydrocarbons.
U.S. Patent Publication 2003-0028060-A1 discloses the modification of alkylation catalyst, such as MCM-22, MCM-49 and MCM-56 with phosphorus to increase the activity and selectivity of the catalyst in the alkylation of aromatic compounds under liquid phase conditions.
However, none of these references contemplate a transalkylation catalyst that comprises zeolite beta catalyst that has been impregnated with phosphorus and exhibits unexpectedly higher relative catalytic activity as compared to conventional zeolite beta for use in alkylation and transalkylation processes.